Adding an additional zone

Custrich56

I currently have a 140,00 BTU Weill-McLain gold cga boiler with a lot of unused extra capacity. The system is hydronic with 1 large circulator for 3 zoned loops. There is also 1 unused zone valve for a radiant system that was never installed. System is on first floor in a 2 story detached home. I have an ABOVE GROUND (totally above) basement that I would like to add heat to using the unused zone valve. Basement is heavily insulated and studded but currently open. 
I would like to add 2 pocket wall fan convectors on opposing sides, diagonally across from each other. One outputting 14,000 BTUs at 190 degrees, one outputting 5200 BTUs at 190 degrees. Both units come with 110/90 degree reverse acting aquastats. I estimate that on an unusually cold day of 10 degrees I would need 18,000 BTUs for this basement.
Is it possible to add this additional loop below the main loop using monoflow tees?

EBEBRATT-Ed

If you are talking about tying into an existing Monoflo loop I wouldn't do that. For two units just pipe them direct return. Take you supply off the zone valve and split it with a tee and go to each heater the same with the return. If using copper pipe 3/4" from the boiler to the tee where you split off to 1/2" to each heater . Same on the return. I would put a balancing valve on the smaller heater heater to balance the flow

Custrich56

Thank you Ed for responding. There is no monoflow loop on the system. Each zone is just a simple closed loop . I am concerned about pressure drop being the fan convectors will be below the main loop.

hot_rod

I would not put them in series in the loop if they have 1/2" copper coils. So a bypass with a valve to regulate flow. If you can make it all accessible for adjusting.



There has been talk of using a diver tee in the fin tube 3/4 but it would not be adjustable.

A homerun with pex would be my first choice. Keeps all the control and zoning options in the mechanical room.

Nice to have iso valves also.

Custrich56

Thanks Bob for your insight. I will consider your recommendations 

hot_rod

Keep in mind also, any fin tube after the added fan convectors will see a lower supply temperature, so lower heat output. Make sure you have adequate fin tube to keep up with the load when the temperature drops through the fan coil units.
If in fact you pull an additional 14,000 btu/hr out mid loop?
Home run would eliminate that concern.

Custrich56

Thanks again Bob. I think I will go with the home run as suggested, adding the isolation valves of course , and balance valve on return of smaller unit. Thanks again.